Tech entrepreneur Martin Ford predicts robots will replace half of U.S. workers over the next 20 years. Here’s why he’s dead wrong.

Technological change is disruptive; new products and companies can lead to the massive decline of other companies and industries. In 1800, 80 percent of Americans worked on the farm; today fewer than 2 percent of the workforce is in agriculture. In the 20th century, manufacturing employment reached a peak of 35 percent of all workers in the early 1950s; today that figure stands at 8 percent.

Although there were many predictions that these shifts would lead to massive unemployment, the long run pattern (interrupted by dips of various sizes due to the business cycle) has been a steady increase in national output. Gross domestic product (GDP) per person has grown from$14,000 (in constant 2009 dollars) in 1950 to $30,000 in 1984 and to $50,000 in 2014.

Tech entrepreneur Martin Ford’s new book,The Rise of the Robots, projects an explosion of technological change. But rather than extolling the benefits of this extra output, he projects that up to 50 percent of workers will be unable to find jobs within 20 years. As a result, his predictions have set off a fresh round of anxieties about the toll of automation on the U.S. economy and American jobs.